In general, a vane pump is a hydraulic oil pump, and as illustrated in FIG. 1, the vane pump includes a cam ring 8 accommodated in a pump housing (not shown) providing a case of the vane pump, a rotor 2 rotatably installed inside the cam ring 8, and a vane 4 installed to be protrudable outside the rotor 2.
Meanwhile, an introduction hole 6a through which oil is introduced and a discharge hole 6b disposed at a side opposite to the introduction hole and through which oil is discharged are defined in the cam ring 8. For example, a power steering vane pump for a commercial vehicle may have a pump efficiency that is remarkably affected according to a size and a shape of a vane and a rotor.
The operation principle of the vane pump is as follows. When the vane 4 is inserted into a vane slot of the rotor 2 at the beginning, and then the vane 4 is discharged from the vane slot due to a centrifugal force caused by rotation of the rotor 2 at the startup, while the vane 4 passes through a space provided due to a shape difference between the rotor 2 and the cam ring 8, oil is introduced through the introduction hole 6a and discharged through the discharge hole 6b. 
As described above, as the rotor 2 has a circular shape, and the cam ring 8 has an inner shape of approximately ellipse, the space provided due to the shape difference between the rotor 2 and the cam ring 8 may be defined, and especially, a theoretical discharge amount may be determined according to an inner profile shape of the cam ring 8.
In detail, when the inner profile shape of the cam ring 8 is not correctly designed, the vane pump may suffer from wear. The design needs to be performed to have a larger volume to avoid the wear occurrence.
Accordingly, a structure capable of reducing the wear of the vane pump and increasing the volume of the vane pump chamber to increase the theoretical discharge amount is demanded.